Topic summary
Necessary condition
Extracted from the Wikipedia article Necessity and sufficiency.
In ordinary English (also natural language) "necessary" and "sufficient" often indicate relations between conditions or states of affairs, not statements. For example, being round is a necessary condition for being a circle, but is not sufficient since ovals and ellipses are round but not circles – while being a circle is a sufficient condition for being round. Any conditional statement consists of at least one sufficient condition and at least one necessary condition.